Molding material feed screw used in molding material supply device of injection molding machine

ABSTRACT

A notched region in which the outer periphery of a screw flight is cut out is provided in a molding material feed screw. A wedge-shaped portion is formed by both a front wall surface of the screw flight and a wall surface of the boundary where the outer periphery of the screw flight is cut out. As a result of rotation of the molding material feed screw, since the wedge-shaped portion advances while pushing aside resin pellets located in the front thereof in two lateral directions of the front wall surface of the screw flight and the wall surface of the boundary where the outer diameter of the screw flight is cut out, entrapment of the resin pellets between the edge of a material supply port of a molding material supply device and the outer periphery of the screw flight is avoided as much as possible.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a molding material feed screw used in amolding material supply device of an injection molding machine.

2. Description of the Related Art

A molding material supply device is arranged between a material supplyport and a hopper or hopper loader of an injection molding machine inorder to supply material to the injection molding machine. Duringmolding by an injection molding machine, a molding material from thehopper or hopper loader, and mainly a resin in the form of pellets, issupplied to the injection molding machine via a molding material supplydevice while being suitably cut into desired portions.

The relationship between the molding material supply device and theinjection molding machine body is explained using FIG. 8.

In FIG. 8, a molding material supply port 23 of a molding materialsupply device 20 is connected to a hopper 22, and a material supply port14 of an injection molding machine body 10 is connected to a materialdischarge port 25 of the molding material supply device 20. A moldingmaterial feed screw 24 driven by a driving device such as a motor 21 isrotatably arranged within the molding material supply device 20. Thismolding material feed screw 24 has spiral grooves formed therein byproviding a screw flight 40.

The injection molding machine body 10 is provided with a heatingcylinder 11 housing a plasticizing screw 15 for filling molten resininto a metal mold clamped by a clamping device (not shown). The heatingcylinder 11 is installed with a heater 13 around the outer peripherythereof for heating the resin supplied to the heating cylinder 11 by themolding material, supply device 20.

Resin pellets 30 (see FIG. 9) used as molding material supplied from thehopper 22 to the molding material supply port 23 of the molding materialsupply device 20 are transported to the material discharge port 25through grooves of the molding material feed screw 24 by rotation of themolding material feed screw 24 driven by the motor 21, transferred tothe material supply port 14 of the injection molding machine body 10,and used for molding. The resin pellets can be suitably apportioned intoamounts required for molding according to the amount of rotation of themolding material, feed screw 24 of the molding material supply device20.

Normally, the molding material supply port 23 of the molding materialsupply device 20 is filled with the resin pellets 30, and the resinpellets 30 are fed inside the molding material supply device 20 whilebeing pushed by the spiral screw flight 40 provided on the moldingmaterial feed screw 24 due to rotation of the molding material feedscrew 24. In order to ensure stable transport of the resin pellets 30,the gap between the outer periphery of the screw flight 40 provided onthe molding material feed screw 24 and the cylindrical inner wall 28 ofa cylindrical space 27 of the molding material supply device 20 ispreferably as small as possible.

However, if the outer diameter of the screw flight 40 approaches theinner diameter of the cylindrical space 27 in order to reduce the sizeof the gap between the outer periphery of the screw flight 40 and thecylindrical inner wall 28 of the molding material supply device 20, aphenomenon occurs in which the resin pellets 30 become entrapped betweenthe edge (material supply port edge 26) of the molding material supplyport 23 of the molding material supply device 20 and the outer edge ofthe screw flight 40 during rotation of the molding material feed screw24.

FIG. 9 depicts a resin pellet 31 entrapped between the material supplyport edge 26 and the outer periphery of the screw flight 40.Furthermore, the material supply port edge 26 serves as the connectionbetween the molding material supply port 23 and the cylindrical space 27(see FIG. 8).

If the resin pellets 30 become entrapped between the material supplyport edge 26 and the outer edge of the screw flight 40, a considerableload acts on the rotating operation of the molding material feed screw24, and a large force (torque) is required to drive and rotate themolding material feed screw 24. In addition, crushing of the entrappedpellet 31 or scraping along the cylindrical inner wall 28 by theentrapped pellet 31 can cause defective molding. Moreover, aconsiderable load may act continuously on rotation of the moldingmaterial feed screw 24 as a result of the entrapped pellet 31 beingpushed into the gap between the cylindrical inner wall 28 and the outerperiphery of the screw flight 40.

In order to avoid this entrapment of the resin pellets 30, entrapment ofresin pellets was conventionally suppressed by forming a notch in theouter periphery of the screw flight 40 in a region of the moldingmaterial feed screw 24 of the molding material supply device 20 whereentrapment occurs.

For example, Examined Japanese Utility Model Publication No. 62-37693discloses a technology of a raw material processing device installedwith a screw feeder in which a gap with the inner diameter of a rawmaterial supply unit was partially increased in size by cutting out aportion of a screw flight near the front edge of a raw material supplyport.

FIG. 10 is an explanatory drawing of the related art in which a notch isprovided in the outer periphery of the screw flight 40 in the moldingmaterial supply device 20.

As shown in FIG. 10, the outer diameter of the screw flight of a regionof the screw flight 40 where entrapment of the resin pellets 30 occursis made to be somewhat smaller than the outer diameter of the screwflight 40 at other portions. In other words, the outer diameter of anotched portion 43 of the screw flight 40 is smaller than the outerdiameter of a non-notched portion 42. In addition, a boundary 41 of thenotch where the outer periphery of the screw flight 40 has been cut outis parallel to an axis of rotation 59 of the molding material feed screw24. As a result of increasing the size of the gap between the screwflight 40 and the cylindrical inner wall 28 of the region whereentrapment occurs as shown in FIG. 10, entrapment of the resin pellet 30can be reduced.

However, when a notch and large gap are provided in a portion of thescrew flight 40, the force that feeds the resin pellets 30 in theforward direction of the molding material supply device 20 ends updecreasing. In particular, since the portion of the level differenceformed in the boundary 41 of the notch of the portion where the notch isprovided in the screw flight 40 is formed parallel to the feed screwaxis of rotation 59, a phenomenon occurs in which the resin pellets 30continue to rotate together with the molding material feed screw 24 as aresult of being pushed into that portion containing the leveldifference.

If the resin pellets 30 continue to rotate together with rotation of themolding material feed screw 24, since the resin pellets 30 wear down andbecome thin due to friction of the resin pellets 30 or the resin pellets30 soften due to heat of friction, the resin pellets 30 end up becomingentrapped in the gap between the outer periphery of the screw flight 40and the inner wall of the cylindrical space 27 of the molding materialsupply device 20. As a result, a large load is imparted to rotation ofthe molding material feed screw 24 or the formation of foreign objectsoccurs during molding.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide a moldingmaterial feed screw used in a material supply device of an injectionmolding machine capable of suppressing the occurrence of entrapmentcaused by rotation of resin pellets together with rotation of themolding material feed screw at a boundary where a notch has been cut outof a screw flight, by forming a notched region in the outer periphery ofthe screw flight provided in the molding material feed screw used in amolding material supply device to provide a large gap between the outerperiphery of the screw flight, and an inner all of a cylindrical spaceof the material supply device.

The molding material feed screw according to the present invention isused in a molding material supply device of an injection moldingmachine, and a molding material is supplied from a first moldingmaterial supply port on the molding material supply device side to asecond molding material supply port on the injection molding machineside. A sharp-angled, wedge-shaped portion is formed in the outerperiphery of the screw flight of the molding material feed screw in thevicinity of the location of the front end of the edge of the firstmolding material supply port, and the outer periphery of the screwflight has a notched region along a prescribed length in the oppositedirection to the direction in which the molding material is supplied tothe second molding material supply port from the wedge-shaped portion.

The outer periphery of the screw flight can be formed in the shape of astep so that the outer diameter of the screw flight in the notchedregion is smaller towards the front and larger towards the rear whenviewed in the direction in which the molding material is supplied to thesecond molding material supply port.

The outer periphery of the screw flight can be formed into a taperedshape so that the outer diameter of the screw flight in the notchedregion is smaller towards the front and larger towards the rear whenviewed in the direction in which the molding material is supplied to thesecond molding material supply port.

A wall surface of the boundary of the notched region where the outerperiphery of the screw flight is cut out that forms one side of thewedge-shaped portion can be provided at a location within a 0.25 pitchin a forward direction from, as well as within a 0.25 pitch in abackward direction from, the location of the front end of the first,molding material supply port when viewed in the direction in which themolding material is supplied to the second molding material supply port.

According to the present invention, by forming a notched region in theouter periphery of a screw flight provided on a molding material feedscrew used in a molding material, supply device, a large gap can beprovided between the outer periphery of the screw flight and an innerwall of a cylindrical space of the resin supply device, and a moldingmaterial feed screw used in a material supply device of an injectionmolding machine can be provided that is capable of suppressing theoccurrence of entrapment caused by rotation of resin pellets togetherwith rotation of the molding material feed screw at a boundary where thenotch is cut out of the screw flight.

BRIEF DESCRIPTION OF THE DRAWINGS

The previously described and other objects and features of the presentinvention will be made clear from the following examples with referenceto the accompanying drawings, wherein:

FIG. 1 is an explanatory drawing of an essential portion of a moldingmaterial feed screw used in a molding material supply device accordingto the present invention;

FIG. 2 is an overhead view of a cross-section taken along line of FIG.1;

FIG. 3 is an explanatory drawing of a first embodiment of a moldingmaterial feed screw according to the present invention;

FIG. 4 is an enlarged view of a leading end in a portion of a screwflight shown in FIG. 3 where the outer diameter of the screw flight issmaller than other portions;

FIG. 5 is a three-dimensional drawing of the molding material feed screwshown in FIG. 3;

FIG. 6 is an explanatory drawing of a second embodiment of a moldingmaterial feed screw according to the present invention;

FIG. 7 is an explanatory drawing of a third embodiment of a moldingmaterial feed screw according to the present invention;

FIG. 8 is an explanatory drawing of the relationship between a moldingmaterial supply device and an injection molding machine body;

FIG. 9 is an explanatory drawing depicting a resin pellet entrappedbetween a material supply port edge and the outer periphery of a screwflight; and

FIG. 10 is an explanatory drawing of the related art in which a notch isprovided in the outer periphery of a screw flight of a molding materialfeed screw.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, an explanation is provided of a molding material feed screwaccording to a first embodiment of the present invention using FIGS. 1to 5.

FIG. 1 is an enlarged view of the portion of the molding material supplydevice 20 in FIG. 8 showing the relationship between a molding materialsupply device and an injection molding machine body. However, a moldingmaterial feed screw 50 shown in FIG. 1 differs from the molding materialfeed screw (molding material feed screw according to the related art)shown in FIG. 8.

In the molding material feed screw 50 shown in FIG. 1, a portion of ascrew flight 51 thereof at which entrapment of the resin pellets 30occurs is cut out and has an outer diameter φD2 that is smaller thanthat of other portions (outer diameter φD1) φD1>φD2) as shown in FIG. 3.By making a portion of the screw flight 51 of the molding material feedscrew 50 to be a notched screw flight 54 as shown in FIG. 3, entrapmentof the resin pellets 30 (see FIG. 5) can be suppressed.

The molding material supply port 23 of the molding material supplydevice 20 has a circular cross-section in the example shown in FIGS. 1and 2. In the case the molding material supply port 23 has a circularcross-section as shown in FIG. 2, entrapment of the resin pellets 30occurs easily at a region on the side indicated with a dashed-two dottedline 29 shown in FIG. 2. Consequently, a portion where the outerperiphery of the screw flight 51 is cut out preferably covers the regionon the side of the dashed-two dotted line 29.

In addition, since the resin pellets 30 are transferred to the front ofthe molding material feed screw 50 by being pushed by the screw flight51 of the molding material feed screw 50, it is not appropriate to cutout the screw flight 51 to the degree that it is completely removed. Thescrew flight 51 is formed so that the screw flight, outer diameter φD2of a notched region 60 where the outer periphery of the screw flight 51has been cut out is made so as to have a larger outer diameter than theroot diameter of the molding material feed screw 50, and so that theresin pellets 30 are able to be transferred forward even in the notchedregion.

Since the region where entrapment of the resin pellets 30 occurs easilyis determined according to the shape of the molding material supply port23, such as that of a round hole, oblong hole or square hole and thelike, and the arrangement of the molding material supply port 23, thenotched region 60 cut out from the outer periphery of the screw flight51 of the molding material feed screw 50 is determined according to theshape and arrangement of the molding material supply port 23 of themolding material supply device 20 used.

Moreover, in the molding material, feed screw 50 shown in FIG. 3, awedge-shaped portion is formed at a starting point 52 of the notch inthe forward direction of the notched region 60 of the screw flight 51where entrapment of the resin pellets 30 occurs most easily as shown inFIG. 4.

In the molding material feed screw 50 shown in FIG. 3, at the startingpoint 52 of the notch in the forward direction of the notched region 60of the screw flight 51 where entrapment of the resin pellets 30 occursmost easily, the wedge-shaped portion provided at the starting point 52of the notch in the forward direction (see FIG. 4) advances whilepushing aside the resin pellets 30 (see FIG. 4) that are in front in thedirection of rotation of the wedge-shaped portion of the starting point52 of the notch in the forward direction due to rotation in thedirection of feed screw rotation 44 of the molding material feed screw50. Furthermore, reference numeral 53 denotes a starting point of thenotch in the backward direction.

A wedge-shaped portion, in which an angle θ formed by a boundary wallsurface 58 where the outer periphery of the screw flight 51 is cut outand a screw flight front wall surface 56 is a sharp angle, is formed asshown in FIG. 4 in the notched region 60 at which the outer diameter ofthe outer periphery of the screw flight 51 is φD2 at the starting point52 of the notch in the forward direction (on the side of the materialdischarge port 25, see FIG. 8). Furthermore, in FIG. 4, referencenumeral 57 denotes a screw flight rear wall surface, while referencenumeral 44 denotes the direction of rotation of the molding materialfeed screw 50. Furthermore, the leading end of the wedge-shaped portionis not required to have a sharp edge in the manner of a blade.

FIG. 5 is a three-dimensional view of the molding material feed screw 50in a first embodiment of the present invention shown in FIGS. 3 and 4

The notched region 60, where the outer periphery of the screw flight 51is cut out, is provided in the molding material feed screw 50. Awedge-shaped portion, which is formed by the screw flight front wallsurface 56 and the boundary wall surface 58 where the periphery of thescrew flight is cut out, is able to advance while pushing aside theresin pellets 30 in front of the wedge-shaped portion in the two lateraldirections of the screw flight front wall surface 56 and the boundarywall surface 58 where the outer diameter of the screw flight is cut outdue to rotation of the molding material feed screw 50 in the directionof feed screw rotation 44.

As a result of the wedge-shaped portion pushing aside the resin pellets30, the resin pellets 30 are forcibly separated into both directions ofthe screw flight front wall surface 56 and the screw flight back wallsurface 57 of the screw flight 51. As a result, the resin pellets 30 arepushed onto a level difference in the surface of the notch boundary (seenotch boundary 41 in FIG. 10), making it difficult for the phenomenonthat occurred in the related art, in which the resin pellets 30 continueto rotate together with rotation of the molding material feed screw 51,to occur, and as a result thereof, entrapment of the resin pellets 30between the edge of the material supply port of the molding materialsupply device and the outer edge of the screw flight can be reduced.

In addition, although the probability of entrapment of the resin pellets30 decreases the smaller the outer diameter φD2 of the screw flight inthe notched region 60 where the outer periphery of the screw flight 51is cut out as previously described, decreasing the outer diameter of thescrew flight weakens the force by which the resin pellets 30 aretransferred in the forward direction of the molding material feed screw50.

Therefore, the result of intentionally making the notch larger in frontof the molding material supply port 23 where the resin pellets 30 areeasily entrapped than in the first embodiment is a second embodimentshown in FIG. 6 and a third embodiment shown in FIG. 7. Referencenumeral 63 denotes a ridge line of the outer periphery of a screw flightof the notched region 60 where the screw flight 51 is cut out.

In the second embodiment shown in FIG. 6, within the region 50 where theouter periphery of the screw flight 51 is cut out, the screw flight in aregion 61 that is a portion thereof in the forward direction is formedinto the shape of a step in which an outer diameter φD3 thereof issmaller than the outer diameter φD2 of the screw flight of a region 62of the remaining portion (φD1>φD2>φD3).

In addition, in the third embodiment shown in FIG. 7, the screw flightof the notched region 60 where the periphery of the screw flight is cutout is formed into a tapered shape in which the outer diameter φD3 tothe front is small, while the outer diameter φD2 to the rear is large(φD1>φD2>φD3).

As is shown in FIGS. 6 and 7, the outer diameter of the screw flight canbe prevented from being made smaller than required by cutting out theouter periphery of the screw flight 51 in a stepwise manner.Consequently, since a loss of force that transfers the resin pellets 30to the front of the molding material feed screw 50 can minimized and theouter diameter of the screw flight 51 in front of the molding materialsupply port 23 where entrapment of the resin pellets 30 occurs moreeasily can be selectively decreased, the occurrence of entrapment of theresin pellets 30 can be effectively suppressed. In addition, as a resultof decreasing the outer diameter of the screw flight in front of thedirection of rotation of the previously described wedge-shaped portion(see FIG. 4), movement of the resin pellets 30, which are pushed asidewhen the wedge-shaped portion advances due to rotation in the directionof feed screw rotation 44 of the molding material feed screw 50, isfacilitated, thereby enhancing the effect of pushing aside the resinpellets 30 by the wedge-shaped portion.

The shape of the outer periphery of the screw flight 51 in the notchedregion 60 where the outer periphery of the screw flight is cut out shownin FIGS. 6 and 7 is selected according to the shape of the moldingmaterial supply port 23 and the arrangement of the molding materialsupply port 23. In the case of the shape of the molding material supplyport 23 being such that the edge of the molding material supply port 23where entrapment of the resin pellets 30 occurs is in the shape of anarrow square hole, a notch in the shape of a step as shown in FIG. 6can be said to be suitable. On the other hand, in the case the moldingmaterial supply port 23 has the shape of a round hole or oblong holehaving a smooth, continuous edge, a notch having a tapered shape asshown in FIG. 7 can be said to be suitable.

Moreover, although not indicated in the description or drawings, theouter periphery of the screw flight 51 in the notched region 60 wherethe outer periphery of the screw flight is cut out may be of a shapethat combines the step-like shape explained with reference to FIG. 6 andthe tapered shape explained with reference to FIG. 7. In addition, inany of the cases of the first embodiment (FIGS. 1 to 5), the secondembodiment (FIG. 6) and the third embodiment (FIG. 7), values for thescrew flight outer diameter φD2 and the screw flight outer diameter φD3may be determined in consideration of the size and entrapment reductionefficiency of the resin pellets 30 presumed to be used.

Moreover, although occurrence of entrapment of the resin pellets 30between the edge of the material supply port of the molding materialsupply device and the outer periphery of the screw flight can bemaximally suppressed by aligning the location where the above-mentionedwedge-shaped portion is provided on the screw flight 51, namely thestarting point 52 of the notch in the forward direction of the notchedregion 60 where the outer diameter of the screw flight 51 is cut out(see FIG. 3), with the front end of the molding material supply port 23,it may also be slightly to the front or back of the location of thefront end of the molding material supply port 23. In consideration ofthe size of typical resin pellets 30, if the starting point 52 of thenotch in the forward direction of the noted region 60 where the outerdiameter of the screw flight 51 is cut out is made to be within a pitchof about 0.25 from the location of the front end of the molding materialsupply port 23 based on the pitch, of the molding material feed screw50, the effect of reducing entrapment of the resin pellets 30 betweenthe edge of a material supply port of a molding material supply deviceand the outer edge of a screw flight can be expected to be adequatelydemonstrated.

Furthermore, the “location of the front end of the molding materialsupply port 23” refers to the location where the front end of themolding material supply port 23 intersects a central axis of rotation 59of the molding material feed screw 50 when the end surface of themolding material supply port 23 is projected towards the central axis ofrotation 59. In other words, it is the location of the end in front ofthe edge of the molding material supply port. In addition, a “pitch ofabout 0.25 from the location of the front end of the molding materialsupply port 23” refers to a location advanced by a pitch of about 0.25in the direction of the central axis of rotation 59 based on theintersected location thereof (based on a pitch of 1 for the gap betweenthe screw flight 51 and screw flight 51 adjacent thereto on the centralaxis of rotation 59).

In the present invention, entrapment of the resin pellets 30 between theedge of a material supply port of the molding material supply device 20and the outer periphery of a screw flight can be reduced in comparisonwith the related art by modifying the shape of the screw flight 51 inthe notched region 60 where the outer periphery of the screw flight 51is cut out of the molding material feed screw 50 of the molding materialsupply device 20.

What is claimed is:
 1. A molding material feed screw used in a moldingmaterial supply device of an injection molding machine, wherein amolding material is supplied from a first molding material supply porton the molding material supply device side to a second molding materialsupply port on the injection molding machine side, and the moldingmaterial feed screw is formed with a sharp-angled, wedge-shaped portionformed in the outer periphery of the screw flight and in the vicinity ofthe location of the front end of the edge of the first molding materialsupply port, and the outer periphery of the screw flight has a notchedregion along a prescribed length in the opposite direction to thedirection in which the molding material is supplied to the secondmolding material supply port from the wedge-shaped portion.
 2. Themolding material feed screw according to claim 1, wherein the outerperiphery of the screw flight is formed in the shape of a step so thatthe outer diameter of the screw flight in the notched region is smallertowards the front and larger towards the rear when viewed in thedirection in which the molding material is supplied to the secondmolding material supply port.
 3. The molding material feed screwaccording to claim 1, wherein the outer periphery of the screw flight isformed into a tapered shape so that the outer diameter of the screwflight in the notched region is smaller towards the front and largertowards the rear when viewed in the direction in which the moldingmaterial is supplied to the second molding material supply port.
 4. Themolding material feed screw according to claim 1, wherein a wall surfaceof the boundary of the notched region where the outer periphery of thescrew flight is cut out that forms one side of the wedge-shaped portionis provided at a location within a 0.25 pitch in a forward directionfrom, as well as within a 0.25 pitch in a backward direction from, thelocation of the front end of the first molding material supply port whenviewed in the direction in which the molding material is supplied to thesecond molding material supply port.